Self-adjusting airscrew



April 7, 1964 V. V. UTGOFF SELF-ADJUSTING AIRSCREW Filed Feb. 28, 1961 INVENTOR l/ADYM l! U TGOF F W? M I M AGENT United States Patent 3,127,938 SELF-ADIJUSTHNG AIRSCREW Vadym V. Utgofi, Dark Harbor, Maine Filed Feb. 2.8, 19611, Ser. No. 92,420 3 Qlaims. (@l. Mil-450.1) (Granted under Title 35, US. Code (1952), see. 256) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a self-adjusting airscrew and more particularly to an airscrew that will automatically adjust to varying relative air velocities.

Present airscrews, when used as propellers, do not compensate for possible variations in relative air velocities acting on the individual blades, such as may be occasioned by cross-winds, sudden gusts, or skids and slips. In the case of a fixed-pitch propeller, no provision is made to compensate in any way for varying speeds of advance of the propeller through the air. In the case of a constant-speed propeller, while provision is made to compensate for varying speeds of advance by utilization of a governor which controls the pitch of all blades simultaneously and equally, no provision is made to adjust individual blades for local variations in wind velocity. In general, when present airscrews are used as helicopter rotors, approximately constant and equal lift is produced by each blade through the use of a tilting rotor, flapping hinges, or mechanical means for cyclic change of blade pitch.

The utilization of the methods mentioned above for operation and control of a conventional propeller or helicopter rotor results in compromises with certain inherent disadvantages, such as for example, an unbalanced thrust causing vibration and introducing a bending moment into the propeller shaft which may result from a cross-wind, gust, skid, or slip and the attendant differences in relative air velocities over each blade resulting therefrom. Also, the individual blades are subjected to a combination of bending stress due to the forces of lift and drag, and tensile stress due to centrifugal force, which requires that the blades be of relatively heavy strength and therefore massive in weight. In the case of helicopter rotors, tilting rotors and flapping hinges can compensate for the difference in relative velocity of airflow of the advancing and retreating blades only over a relatively narrow speed range, while cyclic pitch change mechanisms are complicated and perform their functions echanically so that the blade pitch does not compensate for local airflow velocity variations such as those produced by cross-winds, or sudden gusts. Finally, as in the case of the propeller, the blades are subject to a combination of bending and tensile stresses so that they must be made stronger and heavier than would otherwise be the case.

With the foregoing limitations of the prior art in mind, it is an object of the present invention to provide an airscrew that will be relatively uninfluenced by local variations in wind velocity.

It is another object to provide an airscrew with blades that adjust so as to provide constant and equal lift regardless of relative airflow velocity.

It is yet another object to provide an airscrew, the blades of which are subjected only to tensile loads.

A still further object is to provide a self-adjusting airscrew utilizing a nr'nimum or" moving parts.

Yet another object is to provide a self-adjusting airscrew of increased reliability and ease of operation.

A further object is to provide a simple, self-adjusting airscrew including the property of reversability.

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Other objects and many of the attendant advantages of this invention will be readily appreciated at the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a side view of a helicopter rotor assembly with an attached blade shown in reduced scale;

FIG. 2 is a vertical section taken along a line substantially corresponding to line 2-2 of FIG. 1; and

FIG. 3 is a force diagram, in two dimensions, of an airfoil surface operated according to the present invention.

While a preferred form only of the instant invention is illustrated, it should be understood that various changes or modifications may be made so as to adapt the selfadjusting airscrew described herein to various applications.

Referring to the drawings, in which like numerals designate the same parts throughout the several views, and more particularly to FIG. 1, there is illustrated a device constructed in accordance with the present invention which comprises one or more blades 10, similar to those of a conventional airplane propeller or helicopter main or tail rotor, but having particular properties to be described hereinafter, which blades are mounted in a hub assembly to form a rotating aerodynamic device. The blades lit) are of conventional design except that their mass is so distributed that the center of lift and the center of gravity coincides both in the spanwise and chordwise directions as shown by numeral 11. Along the forward edge of each blade 10 an extension 14 of the feathering axis 13 is provided to facilitate the attachment of the blade to a hub assembly shown generally at 12. The feathering axis 13 is that axis about which the blade will rotate for reasons to be described hereinafter. A rotor mount 15 which may be driven by a reciprocating engine or other power means as desired, which is not illustrated, is provided to support the hub assembly. The outer radial portions of hub assembly 12 are provided with shaft sockets 16 corresponding in number to the number of blades to be attached thereto. The shaft extension 14 of feathering axis 13- is then rotatably mounted within shaft socket 16 and restrained therein by restraining means 17 on the inner end of shaft extension 14. Restraining means 17 and shaft extension 14 ride against bearings 18 contained within shaft socket 16 and which are adapted to restrain horizontal movement of the rotor blade assembly It}. An end plate 20 is fixedly positioned across the outer extremity of shaft socket 16, which plate contains an elliptical opening therein as shown in FIG. 2, which is a cross-section taken along the line 2-2 of FIG. 1. The elongated cross-sectional opening 19 in plate 24} permits a limited horizontal movement of the entire rotor blade assembly, thereby acting as a conventional drag hinge.

It may be seen that the rotor blade lit) is constrained within shaft socket 16 so that it is free to rotate about its feathering axis, and further, it is allowed limited movement in the horizontal plane to the extent that the elliptical opening 19 in the end plate 26 will permit. When the rotor is in operation centrifugal forces will tend to draw the rotor to the outer extremities of socket 16, at which point further movement of the rotor in a lateral direction will be prevented by restraining means 17 coming in contact with bearings 18 which in turn are contained by end plate 20. Thus, as shaft 15 rotates, the rotor blade 10 is unable to move laterally; however, it is completely free to rotate about the feathering axis 13 which extends radially from the rotor mount, and further, limited movement in the horizontal plane is permitted by slot 19 so that to a limited extent the rotor blade will compensate itself for unbalanced drag effects.

The shaft socket 16 is pivotally mounted at 21 to rotor shaft 15 allowing the angle between rotor blade 10 and the horizontal to be varied at will. This angle, which is known as the coning angle, may be controlled by means of control rod 23 connected between the end of plate 20 and the control plate 22. The control plate is slidably mounted on rotor mount 15 so that its movement in the vertical direction will be transmitted by adjustment rod 23 to the shaft socket thus determining socket angle relative to the horizontal. A coning angle control rod 24 may be provided between control plate 22 and any desired actuating means for adjusting the coning angle.

Referring now to FIG. 3, which is a force diagram, it will be appreciated that in operation, with any coning angle other than zero, there will exist for each blade a component of centrifugal force F perpendicular to the blade and acting through its center of gravity. The magnitude of this force will depend on the mass of the blade, which is a constant for any particular blade, the speed of rotation, and the coning angle. This relationship is given by the equation F mRw sine 0 Where F is equal to force, m to mass, R is the radius of the center of gravity of the blade, to is angular velocity, and 0 is the coning angle. Since blade is free to rotate about its feathering axis, this force, acting on the blade, will rotate the blade varying its pitch and thus its angle of attack until the resultant lift force L, which is a function of angle of attack and which acts in a direction opposite to force F, just balances force F leaving a zero resultant force acting in a direction perpendicular to the plane of the blade. Therefore, the only force transmitted to the hub will be the component of centrifugal force T, acting along the feathering axis. The magnitude of this force also depends on the mass of the blade, the speed of rotation and the coning angle as shown by the equation T=mRw cosine 0. It may be easily seen that force T may be broken down into two components, one parallel to the axis of rotation and one perpendicular thereto, the magnitude of each being dependent on the coning angle. The component of this force acting parallel to the direction of the axis of rotation is given by the equation P=mRa sine 0 cosine 0 and is transmitted to the rotating hub solely by tensile forces acting on the rotating blade. It is readily seen, therefore, that the thrust produced by each blade of the self-adjusting airscrew is completely independent of the relative air velocity over the blades, since the angle of attack adjusts automatically to maintain constant lift, and depends only on the mass of the blade, the speed of rotation, and the coning angle.

An inspection of the equation for the component of T which produces thrust P will reveal that the thrust P is dependent on the mass of the blades, the radius of the center of gravity, the speed of rotation and the product of the sine and cosine of 0, 0 being the coning angle. For the smaller angles of 0, it will be realized that the product of sine 0 and cosine 0 is a steadily increasing value as 0 increases, inasmuch as the cosine of 0 remains approximately unity for such angles while the sine is rapidly increasing from zero toward unity. Therefore, as the coning angle is increased and 0 is also increased, all other values remaining constant, the magnitude of P will increase.

This dependency of force P on the magnitude of 0 provides a simple and convenient method of controlling the amount of thrust produced in a vertical direction along the axis of rotation, and therefore, a convenient method of controlling the thrust generated by an aircraft propeller or helicopter rotor.

From the above description it may be realized that many advantages are presented by the instant invention, one of the most important being the fact that the blades produce a constant and equal upward thrust regardless of the relative airflow velocity thereover. This factor may assume considerable importance in the operation of a helicopter at lower altitudes and results from the blades, as they advance and retreat, automatically adjusting themselves as necessary to maintain constant and equal thrust notwithstanding any local variations in wind velocity. Further, the speed of rotation and the coning angle may be selected to obtain most efficient engine operation or minimum blade drag for any operating condition. The thrust may be easily varied over a wide range by simply changing the coning angle.

At this point, it should be noted that the coning angle may be either positive or negative and when this angle is negative the effect will be to produce a resultant thrust in the opposite direction from that shown in FIG. 3. It will be immediately realized that such operation will provide a property of reversability in an airscrew, of the type described herein, which reversability is achieved without subjecting the individual blades to extreme stress variations as occurs in the ordinary propeller. For normal operation of the instant invention, the inclusion of the drag hinge will be sufiicient to compensate the blade for any unbalanced bending moment due to blade drag.

Since the blade pitch is self-adjusting, the instant invention provides a helicopter rotor or aircraft propeller configuration operable without the usual complicated pitch change mechanisms or governors which are normal- 1y found associated with structures of this nature. It should be realized that for even greater simplicity an optimum coning angle may be adapted for a particular use and therefore the mechanism for changing the coning angle may be eliminated.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A self-adjusting airscrew, comprising in combination, a power driven rotatable hub, at least one blade having a feathering axis and being in the form of an airfoil surface, the center of gravity and center of lift of said blade coinciding in both the spanwise and chordwise directions, means for mounting said blade in said hub in radial relation thereto, said mounting means permitting said blade to rotate freely about its feathering axis and permitting limited movement of said blade relative to said hub in the plane of rotation of said blade, controllable m ans attached to said hub for varying the coning angle of said blade whereby the rotation of said hub will produce a component of force normal to the plane of said hub, the magnitude and direction of which force will be determined by the magnitude and sense of said coning angle.

2. A self-adjusting airscrew, comprising in combination, a power driven rotatable hub, at least one blade, said blade being constructed in the form of an airfoil with a feathering axis in the longitudinal direction thereof, the center of gravity and center of lift coinciding in both the spanwise and chordwise directions, means for mounting said blade in symmetrical radial relationship to said hub, said mounting means including means for permitting free rotation of said blade about its feathering axis and limited movement of said blade relative to said hub in the plane of rotation of said blade.

3. A self-adjusting airscrew, comprising in combination a power driven rotor shaft, a hub rotatably mounted on said rotor shaft, at least one blade having a feathering axis, said blade having an airfoil cross section, the center of gravity and the center of lift of said blade coinciding in both the spanwise and chordwise directions, attaching means for mounting said blade to said hub in radial relation thereto, said attaching means comprising at least one socket radially extending from said hub, said socket having a centrally located aperture extending therein, said blade having a shaft extension with an enlarged end portion which is received by said aperture, said blade being free to rotate about said feathering axis within said aperture, a plate having a slot therein attached to the end of said socket portion, said shaft extension extending through said slot thus permitting limited movement of said rotor blade relative to said hub in the plane of rotation and said plate preventing said blade from being thrown radially outward from said socket, bearing means mounted in said socket between said end plate and said enlarged portion of said shaft extension, controlling means attached to said hub for varying the cone angle of said blade whereby the lifting force of said rotor blade will produce an upward component, L, normal to the plane of said blade, the magnitude and direction of force, L, will cancel component F, of the centrifugal force, thus leaving a zero resultant force acting in a direction perpendicular to the plane of the blade.

References Cited in the file of this patent UNITED STATES PATENTS 1,777,630 Vaughn Oct. 7, 1930 1,943,210 De Lavaud Jan. 9, 1934 2,233,747 Riedl Mar. 4, 1941 2,359,265 Hackenthal et a1 Sept. 26, 1944 2,397,154 Platt Mar. 26, 1946 2,755,869 Magill July 24, 1956 FOREIGN PATENTS 934,336 France Jan. 10, 1948 293,932 reat Britain July 19, 1928 

1. A SELF-ADJUSTING AIRSCREW, COMPRISING IN COMBINATION, A POWER DRIVEN ROTATABLE HUB, AT LEAST ONE BLADE HAVING A FEATHERING AXIS AND BEING IN THE FORM OF AN AIRFOIL SURFACE, THE CENTER OF GRAVITY AND CENTER OF LIFT OF SAID BLADE COINCIDING IN BOTH THE SPANWISE AND CHORDWISE DIRECTIONS, MEANS FOR MOUNTING SAID BLADE IN SAID HUB IN RADIAL RELATION THERETO, SAID MOUNTING MEANS PERMITTING SAID BLADE TO ROTATE FREELY ABOUT ITS FEATHERING AXIS AND PERMITTING LIMITED MOVEMENT OF SAID BLADE RELATIVE TO SAID HUB IN THE PLANE OF ROTATION OF SAID BLADE, CONTROLLABLE MEANS ATTACHED TO SAID HUB FOR VARYING THE CONING ANGLE OF SAID BLADE WHEREBY THE ROTATION OF SAID HUB WILL PRODUCE A COMPONENT OF FORCE NORMAL TO THE PLANE OF SAID HUB, THE MAGNITUDE AND DIRECTION OF WHICH FORCE WILL BE DETERMINED BY THE MAGNITUDE AND SENSE OF SAID CONING ANGLE. 